In a typical chemical toner process, such as an emulsion aggregation toner process, the process includes a step of homogenizing or high-shear mixing, an initial slurry to form “pre-aggregated particles” prior to aggregation and coalescence. Homogenization is carried out to evenly disperse a coagulant into the toner slurry and to break up the pre-aggregated particles that form upon addition of the coagulant to a desired average particle size. However, homogenization can be time consuming and energy intensive.
In a typical emulsion aggregation process, the final average toner particle size is about 5.8 μm and the pre-aggregated particle size is about 3.3 μm at room temperatures (about 17-25° C.). As such, to make a toner with a final average particle size of 3 or 4 μm is very difficult or impossible under the current processes because of the relatively large particle size of the pre-aggregated particles. For example, it would be very difficult to make such a toner when beginning with a 3 μm pre-aggregated particle to incorporate all the necessary components and still achieve a narrow geometric size distribution (GSD) while performing the conventional steps to make a toner. However, better image quality and lower toner coverage could be made possible by making toner particles with an even smaller average final particle size.
What's more, the typical emulsion aggregation steps are generally carried out in batch process mode due to the difficulty and expense of developing equipment capable of carrying out a homogenization step in a continuous process mode. As such, continuous processes, as opposed to batch processes, cannot be easily employed for typical emulsion aggregation processes and the economical and process benefits associated with continuous processes, such as increased throughput and automation, cannot be easily realized with current processes.
As a result, there exists a need to develop a continuous toner process with smaller sized pre-aggregated particles that may subsequently be coalesced to achieve much smaller final toner particles.
Also, in a typical emulsion aggregation process, a resin emulsion is made by mixing a resin with a solvent and/or a surfactant. Solvent-free emulsions are desirable because such emulsions result in no waste solvents and as such, can be more environmentally friendly. In addition, in view of increasing costs and regulation associated with waste disposal, it is desirable to avoid toner components associated with materials that cannot be conveniently, cost-effectively, and/or environmentally disposed. However, solvent-free emulsions require an increased surfactant loading, which can inhibit thickening of the slurry and, thus, reduce or inhibit effective homogenization of the slurry particles. This in turn results in high levels of % coarse particles and unacceptable GSDs.
As a result, there exists a need to develop a toner process that can accommodate for high surfactant loaded resin emulsions while still maintaining desirable and usable end products.